Optical isomers, which have the same structural formula, are in a relation of mirror image to each other, since atoms therein have different arrangement spatially. It is well known that medicines that contain optical isomers exhibit considerable differences in efficacy and toxicity. Accordingly, in the Medicine Production Guideline by the Ministry of Health, Labor and Welfare, Japan, it is described that “When the drug is a racemic body, it is desirable that absorption, distribution, metabolism, and excretion behaviors of each isomer are studied.”
When only one of the optical isomers is used as a therapeutic drug, the dosage of the drug can be reduced to increase efficacy per unit and reduction of side effects can be attempted. Therefore, in the field of drug- and biochemistry-related industries and so on, it is becoming an extremely important subject to prepare optically active substances having high optical purity.
Specified dihydroxyheptenoic acid esters including some optical isomers are known to be very effective for the prevention and therapy of hyperlipemia, arteriosclerosis, and so on. Examples of known methods of producing such dihydroxyheptenoic acid esters include methods of producing optically active dihydroxyheptenoic acid esters industrially using packing materials for optical resolution (see, for example, pamphlets of WO95/23125 and WO02/30903).
However, the productivity of the dihydroxyheptenoic acid esters produced by using the conventional packing material for optical resolution remains to be studied and there has been a keen demand for a method for the production of optically active dihydroxyheptenoic acid esters with more excellent productivity.
The present invention provides a method of separating optically active dihydroxyheptenoic acid esters more clearly.